The ground stores and moves huge amounts of water, in the water cycle

Groundwater storage

The ground stores huge amounts of water and it exists to some degree no matter where on Earth you are. The water gets there by gravity. The top layer of the ground is the soil and below that is where true groundwater exists—sometimes called an aquifer. In these layers the rock has many small openings, cracks, and fissures and water occupies all the spaces. People can sometimes drill wells into this region and pull out water for irrigation and drinking.

This picture gives you an idea of how an aquifer works. At a certain depth water saturates all the openings between the rock (sand, in this case) particles. That pool of water you see is a mix of dirt and water (the "aquifer" you see in this picture is more watery than a true aquifer).

The deeper down you go, the rocks become more dense, thus "squeezing" out openings in the rock. Temperatures also get extremely hot further down, which prevents liquid water from existing. Thus, at a certain depth, miles into the Earth, no more liquid water will be found.